In statistics, a meta-analysis refers to methods that focus on contrasting and combining results from different studies, in the hope of identifying patterns among study results, sources of disagreement among those results, or other interesting relationships that may come to light in the context of multiple studies. In its simplest form, meta-analysis is normally done by identification of a common measure of effect size. A weighted average of that common measure is the output of a meta-analysis. The weighting is related to sample sizes within the individual studies. More generally there are other differences between the studies that need to be allowed for, but the general aim of a meta-analysis is to more powerfully estimate the true effect size as opposed to a less precise effect size derived in a single study under a given single set of assumptions and conditions. A meta-analysis therefore gives a thorough summary of several studies that have been done on the same topic, and provides the reader with extensive information on whether an effect exists and what size that effect has.